Hello to you
I'n my part of the world, I often have electrical power failure. I am wondering if it is possible to hook up a 12 volt car battery to a 12 volt led strip or 12v cob. This part I am sure works however would like to automate the process. Because right now I would need to manually hookup the charger to 12V battery when I have house electricity. During power failure I must disconnect manually the charger and connect manually the 12V light.
What is a better automatic solution. Thanks
I am wondering if it is possible to hook up a 12 volt car battery to a 12 volt led strip
Yes. (A fully-charged car battery is nominally 14.4V with no load or a light load, but it should work.)
or 12v cob.
Only if it has a driver circuit. LEDs are powered by constant (or controlled) current, not constant voltage.
...LEDs strips have a current-limiting resistor on each LED... It's generally not practical to use a high-power current-limiting resistor with a high-power LED, although it's equally inefficient either way.
You'd need a MOSFET driver to switch it on/off and some kind of logic inverter (such as another transistor or MOSFET) to pull-down the gate to turn-off the MOSFET while the power is on. And, it would be a good idea to electrically isolate the AC from the low-voltage DC.
Or... An SPDT or DPDT relay with an AC coil could be used to control the DC light while isolating the AC. But, you'd have to power the relay coil 24/7.
Thanks for your input. I have been googling and agree that an AC relay could be helpful here. I do not mind that the relay is powered 24/7.
So I guess an AC relay that is normally closed (No AC power present) could be used to power a 12Volt led strip via car battery.
And a AC relay that is normally open(No AC power present, closed with AC power present) could be used to charge the car battery.
However unsure if on the right track. Do not mind buying ac circuit off amazon or ebay that could assist.
I think this could be used.
Double pole double throw relay. If someone can confirm it would be appreciated. Thanks
Hi,
Sorry but I'm just off to work so can only say that you don't need to use AC control.
Use a diode and a relay with 12V coil.
The diode would have to be rated at more than the maximum output current of the charger, but it means you are not stuffing around with mains voltage AC.
If I get a break at work, I'll post a circuit.
Tom.. 
Circuit as shown will only drive the load while power is available.
Yes the diagram make sense except for the NC/NO relay it should be NC or NO? This part is confusing but the overall idea makes sense to me.
Ok after verification I am in agreement with bluejets previous post.
a relay can be like an A/B switch.
connect the light to the COMMON of any SPDT relay.
connect the 12V output of the CHARGER to the N-OPEN side of the relay
connect the 12v batter to the N-CLOSED side.
connect the coil to your AC or line voltage or house power.
the relay will become energized and change state.
now the relay is energized and the normally OPEN will be closed.
the 12V output from the charger will be fed through the relay to the LED.
if you lose power, the relay fails and the N-CLOSED, that has the output of the battery, will connect to the LED.
this is super simple. all you need to get is either a 12 coil that you can power from the charger output or a line voltage that you connect to the house.
no need to use resistors or diodes or any of that.
just the relay.
opale7000:
Hello to youI'n my part of the world, I often have electrical power failure. I am wondering if it is possible to hook up a 12 volt car battery to a 12 volt led strip or 12v cob. This part I am sure works however would like to automate the process. Because right now I would need to manually hookup the charger to 12V battery when I have house electricity. During power failure I must disconnect manually the charger and connect manually the 12V light.
What is a better automatic solution. Thanks
Hi opale7000,
Why do you need to disconnect the charger and connect the lights if the power fails?
Why not leave both hooked up and here i assume the lights have a switch in the room to turn them on and off.
You seem to indicate the leds will be a seperate/new system to your existing lights.
If the charger is a reasonably good one you can leave it on continuously otherwise i would not leave it on for more than 2 days past fully charging the battery or rusk overcharge (some chargers are strictly charge and disconnect with no facilities to maintain the battery.
Your battery charger should have the following stages Bulk, Absorbtion and Float or Maintainence charge.
Dont forget that batteries will vent EXPLOSIVE and CORROSIVE gas in the event of overcharging. Not good in an enclosed space.
Look into Caravan systems that now run all low voltage lighting and have inbuilt battery and charging systems. There are lots of ideas.
Daz1712:
Hi opale7000,
Why do you need to disconnect the charger and connect the lights if the power fails?
Why not leave both hooked up and here i assume the lights have a switch in the room to turn them on and off.You seem to indicate the leds will be a seperate/new system to your existing lights.
If the charger is a reasonably good one you can leave it on continuously otherwise i would not leave it on for more than 2 days past fully charging the battery or rusk overcharge (some chargers are strictly charge and disconnect with no facilities to maintain the battery.
Your battery charger should have the following stages Bulk, Absorbtion and Float or Maintainence charge.Dont forget that batteries will vent EXPLOSIVE and CORROSIVE gas in the event of overcharging. Not good in an enclosed space.
Look into Caravan systems that now run all low voltage lighting and have inbuilt battery and charging systems. There are lots of ideas.
No need to disconnect charger, I aggree however want to turn on light via battery if AC power failure.
dave-in-nj:
a relay can be like an A/B switch.connect the light to the COMMON of any SPDT relay.
connect the 12V output of the CHARGER to the N-OPEN side of the relay
connect the 12v batter to the N-CLOSED side.connect the coil to your AC or line voltage or house power.
the relay will become energized and change state.
now the relay is energized and the normally OPEN will be closed.
the 12V output from the charger will be fed through the relay to the LED.if you lose power, the relay fails and the N-CLOSED, that has the output of the battery, will connect to the LED.
this is super simple. all you need to get is either a 12 coil that you can power from the charger output or a line voltage that you connect to the house.
no need to use resistors or diodes or any of that.
just the relay.
Agreed however the requirement is to ONLY light the led if there is an AC power failure.
TomGeorge:
Hi,
Sorry, morning coffee hadn't fully soaked in.
Tom..
Ok Looks good. Is the relay called a single pole double throw normally closed or single pole double throw normally open? Or does not matter in that it is just wired accordingly?
The relay is called a single pole, double throw (one wire, switches between two connections)
There are three connections, one is common (C or COM) the other is normaly closed (NC) when the relay is not powered the other is normaly open (NO) anc closes when the relay is powered.
Will the diode not have an impact on the charger? Because there is a minimal voltage drop?
Daz1712:
The relay is called a single pole, double throw (one wire, switches between two connections)
There are three connections, one is common (C or COM) the other is normaly closed (NC) when the relay is not powered the other is normaly open (NO) anc closes when the relay is powered.
Great. finally got it!
Forget everything anyone has said.
You can use a voltage sensitive relay to automatically run lights on battery if AC cuts out. This is used in car setups that run two batteries (one starter and one deep cycle). Look up some videos and guides in that regard and you will hopefully understand. Products are complete and you don't have to risk building anything involving mains power.
INTP:
Forget everything anyone has said.
You can use a voltage sensitive relay to automatically run lights on battery if AC cuts out. This is used in car setups that run two batteries (one starter and one deep cycle). Look up some videos and guides in that regard and you will hopefully understand. Products are complete and you don't have to risk building anything involving mains power.
I disagree.
Circuit and component count that Tom George provided is simple and easy to construct.
There is no mains voltage involved so I don't know where you got that idea.
